DSLR pre-amps are bad. Recording to an offboard audio recorder is ideal, but directly pluggin in is probably still fine for the hobbyist, or for a quick shoot like this.

You actually can attach two of these to a single input, just by using a simple splitter. That has a couple downsides however. First, you can't alter the audio levels separably, requiring you to alter the mic positions to adjust for volume. Second, every piece of equipment you introduce will likely add more noise.

I've included a link to the mic below. I don't get any referral credit, sadly.